The overall goal of this project is developing improved hematopoietic stem cell based therapies to treat primary immune deficiencies. We have a particular interest in chronic granulomatous disease (CGD) and X-linked severe combined immune deficiency (XSCID). Through these studies we aim to increase understanding of the basic biology of trafficking of hematopoietic stem cells and other cells into and out of the bone marrow;to delineate the homeostatic mechanisms that maintain or expand the pool of hematopoietic stem cells;and the mechanisms that induce differentiation of HSC into more mature leukocytes. We also aim to devise improved methods for growing or maintaining HSC in culture without losing reconstitution potential. Also related particularly to allogeneic and matched unrelated donor transplants is to devise new treatments that prevent or treat graft versus host disease. These studies will provide information that will allow therapeutic manipulation of the transplant/engraftment process. There are many clinical settings in which the number of CD34 positive hematopoietic adult human stem cells are limiting (cord blood transplants for example;or settings of gene therapy where the number of gene corrected autologous CD34 positive hematopoietic adult human stem cells are limited). Our studies are currently focussed on, but not limited to the role of HOXB-4 and other upstream and down stream hematopoietic stem cell proliferative signals in maintaining the stem cells population, with a goal of using such information to allow expansion of HSC in culture while maintaining engraftment/reconstitution potential. We have been very interested in the CXCR4/SDF-1 axis and regulatory elements of the system such as CD26 a dipeptidyl peptide IV protease as an important receptor/ligand/downregulatory axis that is very important to enhancing engraftment and to the trafficking of other blood cells, particularly neutrophils and B lymphocytes. In that regard we have been collaborating closely with our colleagues David McDermott and Philip Murphy in LMI/NIAID in studying a group of patients with WHIM syndrome caused by C-terminal truncating mutations that lead to hyperactivity of CXCR4. Finally, we have initiated a program of development and study of induced pleuripotent stem cells (iPSC) derived from somatic cells of patients with PIDs with the goal of using iPSC to study the biology of development of HSC and other blood cells from iPSC and to use iPSC as an in vitro models of the immune defects that are manifested in patients with PIDs. We are particularly interested in delineating the the potential of iPS cells derived from patients with PIDs to differentiate into immune leukocytes such as neutrophils, monocytes and lymphocytes. It is also a part of the goal of this project to communicate information about the biology of HSC, transplantation for PID, graft versus host disease, WHIM syndrome, iPSC models of primary immune deficiencies through publication about primary studies and to publish reviews to educate scientific colleagues and the general public about advances in these areas of study. Published results of our accomplishments toward the goals of this project in the past fiscal year include: 1. Studies of the CXCR4 receptor and its importance in trafficking of HSC and other types of blood cells: We have contributed to work by our colleagues (Brenner laboratory) demonstrating a role for the CXCR4 receptor as being important to the growth and trafficking of human acute myelogenous leukemia cells (Jacobi A et al, Exp Hematol 2010). We have reviewed in detail the biological defects of the CXCR4 receptor and the clinical consequences of truncating mutations that lead to hyperactivity of this receptor as a cause of the immune deficiency known as WHIM syndrome (Kawai and Malech. Curr Opin Hematol 2009). We and our colleagues (Murphy lab) have together shown that some patients with a defect in G6PC3 that causes chronic neutropenia leads also to a WHIM like increase in retention of neutrophils in the marrow with apoptosis in the marrow because of an increased expression of CXCR4 (McDermott et al, Blood 2010). Also together with the Murphy lab we have shown that plerixafor (a potent inhibitor of CXCR4 activity also inhibits the abnormally high activity of C-terminal truncated CXCR4 in WHIM syndrome (McDermott et al, J Cell Molec Med, 2010). This could lead to new treatments for WHIM syndrome. 2. We have shown for the first time that a highly specific agonists (activators) of the Adenosine A2A receptor can prevent graft versus host disease in a single mismatch model of GVHD (Lappas et al, L Leukoc Biol 2010). Since these highly specific Adenosine A2A small molecule agonists are also in commercial Phase I and II clinical trials to treat the inflammation of asthma and chronic obstructive pulmonary disease there is also real potential of this class of agents in the future being applied to the GVHD prevention in the clinic. 3. Together with our colleagues (Dunbar lab;Sorrentino lab) we have shown in a non-human primate transplant model that an in vivo selection system based on gene transfer of O-benzylguanine resistant mutant methylguanine methyl transferase into the transplanted autologous HSC selects only at the progenitor level leading to only transient increases in gene marking of HSC in the animals (Larochelle et al, J Clin Invest 2009). 4. We have together with our collaborator, Dr. Linzhao Cheng at Johns Hopkins University initiated a project to develop iPS cells from patients with primary immune deficiencies, focusing initially on patients with X-linked chronic granulomatous disease (X-CGD) (a PID caused by a defect of microbicidal hydrogen peroxide production by blood neutrophils). We have successfully established X-CGD iPS cells from bone marrow mesenchymal cells;differentiated X-CGD iPS cells into mature neutrophils to demonstrate the defect in oxidase activity;and used gene transfer methods to correct the deficiency in the X-CGD iPSCs such that when differentiated to neutrophils the oxidase activity is restored. This will establish a model that will allow exploration of the potential of applying methods of gene repair to the X-CGD iPS cells to correct the CGD phenotype in neutrophils that arise from the gene corrected iPS cells. This work has great potential for developing future treatments for X-CGD and other primary immune deficiencies.